O'Neill, a native of Youngstown, Ohio, became intrigued with acting when he was teaching sixth grade and taking theater classes at Youngstown State University in his spare time.

Seven years later, O'Neill decided to pursue acting as a profession, so he moved to New York and got a job as a bus boy. His first break came when he was understudying the lead in the Broadway play "Knockout." True to theatrical legend, the lead left the show, the understudy took over the role and the rest is history.

His other stage credits include appearances off-Broadway and in regional productions of "The Front Page," "A Street Car Named Desire" and "Of Mice and Men."

On film, O'Neill co-starred in the Amblin Entertainment film "Little Giants," along with Rick Moranis; starred with Nick Nolte in "Blue Chips;" and was featured in "Wayne's World" and "Wayne's World II." He has also appeared in "Cruising," "Dogs of War," "Disorganized Crime," "K-9," "Sibling Rivalry" and in the title role in "Dutch." Recently, O'Neill starred in the Tiffany Theater's production of David Mamet's play "Lakeboat."